430 THE HISTORY OF BIOLOGY 



single-celled organisms — namely, the bacteria or Schizomycetes, which, 

 as is well known, have since been found to play a most vital part in human 

 life and which have accordingly been investigated ever since the middle of 

 the last century as a special field of research. In connexion with this branch 

 of research there have existed a number of theoretical problems of the greatest 

 significance; the problems of spontaneous generation, fermenting processes, 

 and the origin of various diseases. The problems of the causes of disease 

 can of course be dealt with only cursorily here; they have of old formed a 

 science of their own — • pathology. The questions of spontaneous generation 

 and the fermenting process, on the other hand, have possessed immense 

 theoretical interest and on the decisive occasion mentioned below their 

 treatment has happened to coincide. We may therefore suitably begin our 

 review of the history of bacteriology with a glance at these two questions. 



Bacteriology and spontaneous generation 

 The belief in spontaneous generation has been mentioned on various oc- 

 casions in the foregoing: how the earlier naturalists generally believed that 

 the lower animals, especially such as appeared suddenly and possessed more 

 or less the characters of parasites or vermin, could arise through some kind 

 of transmutation process in lifeless matter; Aristotle believed that fleas 

 and mosquitoes originated in putrefying matter — a belief with which even 

 Harvey at least partially associated himself, while van Helmont had seen 

 rats arise out of bran and old rags. In the seventeenth century Francesco 

 Redi (16x6-98), court physician and academician in Florence, proved that 

 worms in rotting meat arise, not in consequence of the putrefaction, but out 

 of eggs laid by flies on the meat; if the latter is protected with thin cloth, no 

 worms arise in it, in spite of the putrefaction. On the other hand, Redi be- 

 lieved in the spontaneous generation of intestinal worms and gall-flies. For 

 theoretical reasons Swammerdam denied spontaneous generation; the doc- 

 trine of preformation that he founded actually precluded any belief in this 

 kind of propagation and during the greater part of the eighteenth century 

 held it in discredit. Nevertheless Buffon, as we have seen in a previous sec- 

 tion, believed in a spontaneous generation through minute life-units scattered 

 throughout the universe and was supported in his belief by his friend the 

 English microscopist Needham; and Lamarck associated himself with this 

 view. On the other hand, Spallanzani, the preformationist, strongly op- 

 posed the doctrine of spontaneous generation and sought to prove that by 

 boiling organic elements in air-tight vessels it was possible to prevent living 

 creatures from arising in them. This theory was put to practical use some 

 decades later by a French chef, Appert, who invented the still commonly 

 practised hermetical inspissation of food. A French physicist, however, 

 found out that the air in the preserving jars lacks oxygen — this element is 

 really consumed by oxidation processes in the contents — and concluded 



